Note: Descriptions are shown in the official language in which they were submitted.
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Title of the invention
Metallurgical reactor for the production of cast iron
Background and summary of the invention
The present invention relates to metallurgical
reactors, and more particularly so-called "smelter"
metallurgical reactors suitably for carrying out a cast
iron production process forming part of the group of
processes known as "smelting reduction" processes.
According to this group of processes, the cast iron is
produced from: a material containing iron, for example
iron ore and/or other reducible metal oxides such as
manganese, nickel, chromium, etc., where applicable
pre-heated and/or pre-reduced; a carbon-based reducing
material, for example coal; a comburent gas containing
oxygen, for example industrial oxygen. The products of
the process are: liquid cast iron composed of an alloy
of iron and other metals with a high concentration of
carbon in solution form; the liquid slag, mainly
composed of calcium, silicon, magnesium and aluminium
oxides, and a gas containing sizeable fractions of
carbon monoxide and carbon dioxide resulting from the
reduction and combustion reactions.
The reactor according to the present invention is
essentially composed of a metal casing internally
lined, at least partially, with refractory material and
provided, in the region of the top closure, with a duct
through which the material containing iron or other
reducible materials, for example iron ore, previously
heated to a high temperature and partially reduced in a
solid-state direct reduction reaction, for example a
rotating-hearth furnace, is introduced.
In this metallurgical reactor it is required to
perform efficient cooling of the ore supply duct both
to protect it from the high temperatures and the damage
resulting therefrom and to prevent adhesion, inside and
outside thereof, of semi-molten materials and slag
which would prevent the descent of the materials and
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would negatively affect regular execution of the
process. The solution used in order to perform said
cooling, which is known as "water jacket", consists in
surrounding this duct with a cavity inside which a
cooling fluid flows. This solution may be regarded as
being adopted from other metallurgical applications
which are characterized by similar environmental
conditions (for example oxygen lances for steel plant
converters) where this problem is commonly solved by
cooling, usually with water, the product which enters
into the reactor.
One of the main problems in these reactors is that
of ensuring both the regular descent of the charge
material into the underlying slag bath and the
elimination or reduction to a minimum of the material
lost as a result of entrainment by the gases flowing
out from the reactor.
In accordance with a main characteristic feature
of the present invention, this problem is solved by
providing, in the bottom terminal part of the said
material loading duct, a series of nozzles for blowing
in compressed gas, for example air, steam or nitrogen,
in order to create a descending gaseous curtain around
the charge material outflow opening, which assists
regular descent of the said material, facilitating its
introduction into the underlying liquid slag bath.
Moreover, owing to the presence of these gaseous jets,
in the vicinity of the outflow opening of the duct a
dynamic vacuum is created, this vacuum counteracting
any tendency of the process gas to rise back up through
the duct during pressure transient peaks of the reactor
due to the natural fluctuations in the process.
In accordance with a further feature of the
present invention, the axis of the terminal part of the
said material loading duct is advantageously inclined
with respect to the vertical in the direction of the
walls of the reactor and means are provided in order to
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rotate said duct part about a vertical axis so as to
distribute the ferrous material the whole way around
the chamber of the reactor, so as to prevent
accumulation thereof in the central zone where there is
greater turbulence, favouring at the same time
introduction thereof into the underlying liquid slag
bath.
The reduction smelting reactors of the type
according to the invention are generally equipped with
means for the injection of comburent gas, in some cases
performed with lances which are suitably directed and
arranged on at least two levels. In the reactor
according to the present invention, via the lances
positioned at a lower level (reducing zone), namely at
the level of the reactor crucible, or via suitable
lances positioned in the vicinity thereof, coal of
suitable grain size is blown into the mass of molten
cast iron by means of a suitable carrier gas.
The side walls and the bottom of the reactor are
lined with refractory material suitable for containing
the liquid phases of the process. To ensure efficiency
of the process, an intense circulation of the liquid
slag is required between the upper zone or oxidising
zone and the bottom zone or reducing zone. This
circulation obviously involves a high degree of heat
exchange as a result of convection between the slag and
the refractory lining which contains it. This,
combined with the chemical aggressiveness of the liquid
slag with respect to any refractory material with which
it comes into contact, is a factor which greatly
influences the duration of the refractory lining and,
basically, in most of the already known smelting
reduction processes is the main unresolved problem
preventing commercialisation thereof.
In accordance with a further characteristic
feature of the present invention, in order to overcome
this problem, cooling elements are arranged in the wall
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section situated opposite the slag bath and the slag
bath/cast iron transition zone, said elements being
intended to remove the heat from the bath with an
intensity such as to cause solidification of the slag
and therefore prevent erosion of the refractory
material, to a depth of penetration of said erosion,
known as "freeze 'Line", of acceptable magnitude, namely
sufficient for ensuring the structural stability of the
remaining wall.
Advantageously, these cooling elements consist of
plates made of metal with a high thermal conductivity,
for example copper, formed preferably from a laminate
in order to take advantage of the optimum mechanical
properties and the improved thermal conductivity,
compared to copper produced by means of casting, and
consisting of solid metal on the inside of the casing
and having formed in them channels through which the
cooling fluid passes on the outside of the casing. The
dimensions of these elements have been optimised in
order to achieve various objectives: sufficient removal
of heat in the specific slag turbulence conditions
required by the process; keeping the temperature of the
metal (copper) below the critical value for the long-
term stability of its metallurgical properties;
sufficient mechanical strength for interacting, without
causing damage, with the surrounding refractory
material during each operating stage, including the
transient phases; easy replacement without the need to
empty the reactor; suitable configuration for keeping
the refractory material in position even when partly
worn; lower weight (and consequently cost) per unit of
surface area of the cooled wall; easy mechanical
machining.
The top part of the reactor, above the liquid
bath, is surrounded by cooled refractory or metallic
walls and is closed at the top by a cooled metallic or
refractory cover having formed in it an opening for
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outflow of the gases produced by the process and
destined for processing and purification plants. The
gas thus produced, which still contains a sizeable
fraction of carbon monoxide, may be used, for example,
5 as fuel in the pre-reduction rotating-hearth furnace.
In one aspect, the invention provides a
metallurgical reactor for the production of cast iron
consisting of a metal casing internally lined, at
least partially, with refractory material, said
metallurgical reactor comprising:
a lower zone for containing molten metal, a middle
zone for containing slag and an upper zone for being
substantially free from molten metal and slag;
a first series of lances for injecting comburent gas
and coal of suitable grain size in the lower zone of
the metallurgical reactor;
a second series of lances for introducing comburent
gas into the middle zone of the metallurgical reactor;
a crucible for collecting cast iron, the crucible
being arranged in the lower zone of the metallurgical
reactor;
a duct for introducing ferrous material into the
metallurgical reactor;
wherein:
an ore outflow opening in a bottom terminal
part of said duct is arranged so as to introduce
the ferrous material at high temperature into the
upper zone of the metallurgical reactor, said
ferrous material being introduced into the
metallurgical reactor by gravitational force; and
said duct is provided with suitable cooling
means, said duct is further provided with nozzles
for blowing in compressed gas in the upper zone
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5a
of the metallurgical reactor, said nozzles being
arranged in the bottom terminal part of said duct.
Brief description of the drawings
Further objects and advantages of the present
invention will be understood more clearly during
reading of the following description considered by way
of a non-limiting example with reference to the
accompanying drawings in which:
Fig. 1 is a side elevation and sectioned view of a
metallurgical reactor for the production of cast iron
according to the present invention, provided centrally
with a duct for supplying iron ore;
Fig. 2 shows a side elevation and sectioned view
of the supply duct according to Fig. 1;
Fig. 3 shows a perspective view of an annular end-
piece fixed to the bottom end of the supply duct
according to Fig. 2;
Fig. 4 shows a side elevation and sectioned view
of a part of the bottom end of the duct according to
Fig. 2, with the associated annular end-piece sectioned
along the line IV-IV in Fig. 3;
Fig. 5 shows a side elevation and sectioned view
of a part of the bottom end of the duct according to
Fig. 2, with the associated annular end-piece sectioned
along the line V-V in Fig. 3;
Fig. 6 shows a side elevation and sectioned view
of a variant of the present metallurgical reactor for
the production of cast iron; and
Fig. 7 shows a plan view of the metallurgical
reactor according to Fig. 1, sectioned along the line
VII-VII in Fig. 1.
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5b
Description of the preferred embodiments of the
invention
With reference to the accompanying figures and in
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particular to Fig. 1 thereof, 1 denotes the metal
casing of the reactor, having an approximately
cylindrical shape. This casing 1 is lined internally
at least partially with a refractory material R
suitable for containing the reacting materials. In the
reactor shown it is possible to distinguish three zones
containing liquid with a density decreasing from the
bottom upwards, namely the liquid cast iron bath 2
contained in the crucible 101, the transition zone 4
for the cast iron 2 and the actual slag 6, both
contained inside an approximately cylindrical casing.
The reactor wall has, formed therein, level with said
transition layer 4 a hole 110 communicating with an
external "calming" well 3 which allows settling of the
two phases 2 and 4 and separation from each other as a
result of overflow, by means of a suitable diaphragm
210 consisting of two different sections 10, 10' of the
said well, for extraction said phases from the reactor.
In the example shown, said extraction occurs
continuously, on the basis of the principle of
"communicating vessels" following overspill of the two
liquid phases 2 and 4 from suitable overflow openings
310, 310' in the walls of the well 3. The system thus
devised is self-regulating both as regards maintaining
the overall level of the molten phase in the reactor
and as regards the relative proportion of the two
phases 2 and 4. In fact, a variation in the overall
level of the two phases inside the reactor, according
to the principle of communicating vessels, is produced
by a greater proportional overspill from the well 3
with a consequent greater throughput of liquid
extracted from the reactor which brings back the level
to the desired value. An increase in the relative
proportion of one of the two liquid phases inside the
reactor produces a corresponding vertical displacement
of the "transition zone" 4 in such a way as to favour
the outflow of a richer liquid of the phase which is
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prevalent in that moment, thus readjusting the relative
proportion of the two phases to the desired value. A
layer essentially consisting of the slag phase 6 is
situated above the zone of transition between the two
liquid phases.
12 and 13 denote lances for injecting a comburent
gas (lance 12) or a gas in combination with particles
of coal (lance 13) . The introduction, via the lance
13, of a comburent gas and carbon, together with the
associated carrier gas, produces an intense turbulence
at the interface between the two liquid phases,
resulting in a zone of intense mixing of the slag with
droplets of cast iron and particles of carbon. This
zone is the site where most of the reduction processes
occur. Part of the heat required for these
(endothermic) reactions to take place is provided by
the combustion of the carbon with the oxygen injected
into the same zone. Since the reactions for reduction
of the metal oxides must take place in this zone, the
only product from combustion of the carbon which is
thermodynamically stable is carbon monoxide. From an
energy point of view, it is known that that combustion
of carbon with CO releases a much smaller amount of
energy than carbon with 002. Consequently, with this
sole combustion product, the amount of carbon 'which
must be used in order to sustain the process in terms
of energy would be very high. For this reason the
lances 12 are provided at a higher level, said lances
having the function of completing the combustion by
converting at least part of the CO into 002 with the
corresponding release of energy. In this so-called
"oxidising" zone, the reduction reactions do not take
place. The presence of the slag 4 between the two
zones creates an isolating layer which is sufficient
for the two (reducing and oxidising) environments to
coexist with the minimum amount of interference. On
the other hand, in. order for the heat released in the
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oxidising zone to be used efficiently it must be
transported into the reducing zone without dispersion
elsewhere, for example in the outgoing gases and
without producing local overheating, which would be
damaging for the life of the reactor. This objective
may be achieved both by ensuring there is an intense
circulation within the slag phase, which circulation is
activated by the introduction of comburent gas at a
high pressure from both the lance levels 12 and 13, and
by directing said lances downwards, so as to induce the
necessary circulation of the slag. Said turbulence,
moreover, favours the incorporation of the ferrous
charge into the liquid bath and its rapid liquefaction.
In order to counteract the negative effect of the
abovementioned turbulence on the duration of the
refractory lining, in the region of both the slag-metal
transition zone 4 and the slag zone 6, a series of
cooling plates 11 made of metal having a. high thermal
conductivity are provided, being suitably mounted in
the refractory lining itself, as described below.
Fig. 7 shows a cross-sectional plan view, along
the line VII-VII of Fig. 1, of the middle zone 201 of
the reactor 1. This cylindrical middle zone 201 is
lined with a series of blocks 501 of refractory
material suitable for containing the liquid phases of
the process. As mentioned, the efficiency of the
process requires an intense circulation of the liquid
slag between the upper oxidising zone and the bottom
reducing zone. This circulation obviously implies a
high thermal exchange between the slag and the
refractory lining which contains it. This, together
with the chemical aggressiveness of the liquid slag
with respect to any refractory material with which it
makes contact, greatly influences the duration of the
refractory lining and, basically, in most of the
already known smelting reduction processes, constitutes
the main unresolved problem preventing these processes
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from being commercialised. In order to overcome this
problem, in the reactor according to the present
invention, the wall section situated opposite the slag
bath and the slag bath/cast iron transition zone is
provided with cooling elements 11 intended to remove
the heat from the bath with an intensity such as to
cause solidification of the slag and therefore stop
erosion of the refractory material, to a depth of
penetration of said erosion, known as "freeze line", of
acceptable magnitude, namely sufficient for ensuring
the structural stability of the remaining wall.
These cooling elements consist of plates made of
metal with a high thermal conductivity 11, for example
plates of copper, formed preferably from a laminate and
consisting of solid metal on the inside of the casing
and having formed in them channels 23 through which the
cooling fluid, for example water, passes on the outside
of the casing. The design of these elements has been
optimised in order to achieve various objectives:
sufficient removal of heat in the specific slag
turbulence conditions required by the process; keeping
the temperature of the metal (copper) below the
critical value for the long-term stability of its
metallurgical properties; sufficient mechanical
strength for interacting, without causing damage, with
the surrounding refractory material during each
operating stage, including the transient phases; total
safety as regards accidental leaks of coolant; easy
replacement without the need to empty the reactor;
suitable configuration for keeping the refractory
material in position even when partly worn; lower
weight (and consequently cost) per unit of surface area
of the cooled wall; easy mechanical machining.
Said plates 11 are advantageously housed inside
pockets formed in the refractory wall 501. A
refractory paste with a high thermal conductivity is
arranged in the free space between said plates and said
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wall, said paste forming a layer 601 able to ensure
firm contact and consequent optimum transmission of the
heat between plate and wall. A layer 701 of insulating
material, which protects said metal casing from
5 excessively high temperatures, is arranged between the
wall 501 and the outer metal casing 801.
These plates 11, see for example the cross-section
of the plate 111, each have a part which protrudes from
the metal casing of the reactor and inside which the
10 pipe 23 for circulation of a coolant is inserted,
usually water. This system allows: removal, from the
bath, of a very high specific thermal flow without
damaging the actual plates and the refractory material;
maintenance of the thermal flow exchanged between water
and plate well below the critical value at which
boiling starts; prevention of any risk of accidental
spillage of water inside the reactor, even in the case
of damage of the plate part which is most exposed to
the stresses causes by the process, owing to the fact
that the water flow pipe 23 is kept outside the casing
1 of the reactor; easy inspection and replacement of
the plates 11; where necessary, sliding of the plates
11 in keeping with any thermal expansion of the wall,
ensuring good contact between plate 11 and refractory
material.
The free space 5 of the internal volume of the
reactor above the liquid bath forms a zone for
"freeing" the gas produced by the process from the
carbon dust and droplets, allowing the discharging
thereof from the reactor with reduced loads of
suspended material. In this zone, the thermo-chemical
stresses on the internal lining are less than those of
the liquid zones. Therefore the side walls and the
vault of said zone may be designed using conventional
techniques such as direct "water screen" cooling on the
outside of the casing or indirect cooling by means of a
"membraned wall" (consisting of steel water-cooling
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pipes welded together so as to form a continuous wall).
In the example shown, the side walls of this zone are
lined with a uniform layer of refractory material R,
while the cover 401 is made using the technique of a
membraned wall. This cover has, extending from it, a
chimney 8 for removal of the exhaust fumes destined for
plants for further processing and a duct 9 which is
positioned centrally and from which the iron ore is fed
into the reactor.
Fig. 2 shows a cross-section through. a portion of
the duct 9 for feeding iron ore into the reactor. This
duct 9 comprises: a central channel 109 for supplying
said ore; a first outer jacket 309 coaxial with said
central duct 109 and connected to a pipe 14 for
supplying a cooling fluid (usually water); a second
outer jacket 409 coaxial with said first jacket 309 and
connected to a pipe for blowing in gas under pressure,
for example, air, steam or nitrogen; a third outer
jacket 509 coaxial with said second jacket 409 and
connected to a pipe 16 for discharging the cooling
fluid, and a bottom annular end-piece 209, for closing
off the various jackets 309, 409, 509 for the purposes
described below. The cooling fluid has the function of
both protecting the duct 9 from the high temperature
and from the damage resulting therefrom and of
preventing adhesion, on the inside and outside thereof,
of semi-molten material and slag which would prevent
descent of the material and negatively affect regular
execution of the process.
With reference to Fig. 3, this shows the annular
end-piece 209 which is fixed to the bottom end of said
duct 9. This annular end-piece 209 has a bottom flange
609 on which a sleeve 709 is integrally formed, said
sleeve having along the whole of its circular perimeter
a series of radial through-holes 17 which are formed
transversely with respect to the associated side wall
and which connects together the cavities 309 and 509
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for circulation of the cooling fluid, and a series of
vertical holes or nozzles 18 communicating with the
cavity 409 for blowing in the compressed gas. These
through-holes 17 are arranged at a certain distance
from each other and a nozzle 18 is provided between
each pair of said horizontal through-holes 17.
The purpose of said nozzles 18 is that of creating
a gaseous curtain descending around the opening for
outflow of the charged material which facilitates the
proper descent of the said material, facilitating its
introduction into the underlying liquid slag bath and
preventing or reducing to a minimum the loss of
material as a result entrainment by the gases flowing
out from the reactor. The presence of the gaseous jets
moreover produces in the vicinity of the outflow
opening of the duct a dynamic vacuum which prevents any
tendency of the process gases to flow back up through
the duct during transient pressure peaks of the reactor
due to the normal fluctuations in the process.
Fig. 4 shows a cross-section through the duct 9,
in the vicinity of the annular end-piece 209 and
opposite any one of the horizontal through-holes 17,
along the line IV-IV in Fig. 3. In this Figure, it is
possible to observe the flow path of the cooling fluid
in the duct 9, which, introduced via the corresponding
supply pipe 14 shown in Fig. 2, firstly descends along
the inner jacket 309, passes through the horizontal
through-holes 17 of the annular head 209, rises back up
along the outer jacket 509 and finally emerges from the
discharge pipe 16 in Fig. 2. The bottom flange 609 of
this annular end-piece 209 is fixed by means of welds
19 to the bottom edge of the outer wall of the outer
jacket 509 and to the bottom edge of the wall of the
central channel 109, while the upper sleeve 709 of said
annular end-piece is fixed by means of other welds 20
to the walls of the middle jacket 409.
Fig. 7 shows another cross-section through the
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duct 9 in the vicinity of the annular end-piece 209 and
opposite any one of the vertical nozzles 18, along the
line V-V in Fig. 3. The gas under pressure supplied by
the associated pipe 15 in Fig. 2 descends along this
middle jacket 409 and finally emerges from the annular
end-piece 209 of said duct 9 through said nozzles 18.
Fig. 6 shows a variant of the metallurgical
reactor according to the invention. According to this
variant, the duct 9 for supplying pre-reduced hot ore
and blowing in gas under pressure is composed of a
vertical upper section 9' and a bottom section 911
having a certain inclination with respect to said
vertical section 9'' . Said inclined section 9'' is
provided at the bottom, in a manner entirely similar to
that described above, with the annular end-piece 209
which has horizontal through-holes 17 for circulation
of the cooling fluid and nozzles 18 for blowing in the
compressed gas, and both said sections 9' and 9'' of
said duct 9 are provided with the inner jacket 309 and
outer jacket 509 for passage of the cooling water and
with the middle jacket 409 for blowing in compressed
gas. The vertical section 9' of said duct 9 is
connected, by means of known transmission means 21, to
a motor 22 having the function of causing rotation of
said section 9' and therefore also said inclined
section 9'' integral therewith. Owing to rotation of
the supply duct 9, the ore is discharged from the
inclined section 9'' against the side walls of the
reactor, instead of in the central zone; in this way
the movement of the liquid slag 6 activated by the
lances 12 and 13 favours on the one hand incorporation
of the pre-reduced ore in the said slag bath 6 and on
the other hand reduces to a minimum the risk of
entrainment of fine particles of said ore inside the
gas evacuation duct 8 as well as backflow of process
gases inside the supply duct 9, since said gases are
mainly emitted from the central zone of the reactor.
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Moreover, the ore which, during rotation of the duct 9,
accumulates against the inner walls of the reactor also
has a protective function preventing corrosion of the
refractory material lining of said walls.
Obviously, the present invention is not limited to
the embodiments illustrated and described, but
comprises all those variants and embodiments falling
within the scope of the inventive idea substantially as
claimed below.
Thus, for example, the terminal part of the duct
9, which is made to rotate by the motor 22, as
described with reference to Figure 6 in the drawings,
instead of being provided with an inclined duct section
9 ', is provided with a deflector which is arranged
inside it and integral with the duct 9 itself and which
deviates the falling trajectory of the ferrous material
in the direction of the side wall.
